Three-phase furnace transformers are used in applications requiring currents in orders of magnitudes approximating 100 K amperes. The furnace transformers are used for supplying arc furnaces with substantially high currents with voltages in the order of a few hundred volts.
The conventional method of wiring the three-phase low-voltage windings for furnace transformers is in a closed delta configuration. Because of the high currents involved, thick electrical conductors, such as bar conductors, are used for carrying the high currents from within the transformer to the transformer outer terminals. The present method of manufacturing furnace transformers consists in bringing the bus bar connectors from the different low-voltage winding legs out to the top of the transformer with the delta unclosed. Every furnace transformer, therefore, must be custom wired by the user. The custom wiring includes closing the delta by means of a plurality of bus bar connections with the bus bar contacts external to the transformer casing. Due to the large current passing through the bus bar contacts the externally exposed contacts and connectors may have to be supplied with supplemental cooling to prevent overheating during periods of high current usage.
The purpose of this invention is to provide means and methods for manufacturing a furnace transformer having low-voltage windings in a closed delta configuration with minimum losses. The internally closed delta furnace transformer of the invention also provides means for integrally cooling the bus bar.